Semiconductor device and manufacturing method for silicon oxynitride film

ABSTRACT

The present invention provides a semiconductor device comprising: a silicon based semiconductor substrate provided with a step including an non-horizontal surface, a horizontal surface and a connection region for connecting the non-horizontal surface and the horizontal surface; a gate insulating film formed in at least a part of the step; and a gate electrode formed on the gate insulating film, wherein the entirety or a part of the gate insulating film is formed of a silicon oxynitride film that contains a rare gas element at a area density of 10 10  cm −2  or more in at least a part of the silicon oxynitride film.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is related to Japanese application No.2002-360865 filed on Dec. 12, 2002, whose priority is claimed under 35USC §119, the disclosure of which is incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a semiconductor device and amanufacturing method for a silicon oxynitride film. More specifically,the present invention relates to a semiconductor device such as a MOStransistor which is formed on a semiconductor substrate having a threedimensional structure, and a manufacturing method for a siliconoxynitride film.

[0004] 2. Description of the Related Art

[0005] Semiconductor devices such as MOS transistors and memory cellshave been miniaturized according to the scaling rule proposed by J. R.Brews for the purpose of implementation of high integration. However,there are great problems that occur in actual devices as miniaturizationprogresses, such as an increase in a leak current due to reduction inthe thickness of a tunnel insulating film, an increase in a diffusionresistance due to reduction in junction depth Xj of source/draindiffusion layers, occurrence of short channel effect, and reduction inthe withstand voltage against punch through between sources and drains.

[0006] In order to solve such problems, there have been proposed threedimensional semiconductor devices wherein semiconductor substrates areprocessed into three dimensional forms so as to secure effectivedimensions of the elements while reducing the projection areas of thedevices. It is explained by FIG. 32 that a technique of utilizing astructure had a trench formed in a semiconductor substrate to work as achannel of a MOS transistor and described in Japanese Unexamined PatentPublication No. HEI 5(1993)-102480 as an example of the above-describedconventional art.

[0007] The MOS transistor of FIG. 32 has a gate oxide film 20 on thesurface of a trench (0.4 to 0.6 μm in depth) in a first conductive typesilicon substrate 1 and a gate electrode material is filled into thetrench via a gate oxide film 20, whereby a trench type gate 6 is formed.Furthermore, a second conductive type source 8 and a drain 9 are formedon both sides of the trench type gate 6. At least one of the source 8and the drain 9 is adjacent to a first conductive type impurity region10 in the direction of the depth of the substrate. The first conductivetype impurity region 10 has an impurity concentration higher than thatof the silicon substrate 1. At least a part of the channel region ofthis MOS transistor is formed in the part other than the firstconductive type impurity region 10.

[0008] With the above-described configuration, it is possible to expandthe channel region in the direction of the depth of the semiconductorsubstrate. Furthermore, the area where the gate electrode is arrangedcan be reduced while preventing the reduction in a threshold voltage dueto a short channel effect and deterioration of an off current. Inaddition, a depletion layer can be suppressed from extending from thesource 8 and the drain 9 so as to increase the withstand voltage againstpunch through.

[0009] The sides of the trench (non-horizontal surfaces) correspond to a(110) plane of the silicon substrate, the connection regions where thesides of the trench make contact with the bottom correspond to a (111)plane, and the bottom of the trench (horizontal surface) corresponds toa (100) plane in the above-described structure. Herein, the gate oxidefilm is formed according to a thermal oxidation method and, in such acase, it is known that more interface levels exist between the siliconsubstrate and the gate oxide film in the (110) and (111) planes than inthe (100) plane. Therefore, the interface levels that exist in the sidesand in the connection regions significantly affect the characteristicsof the semiconductor device such that they make lower mobility ofcarriers and they make a threshold voltage fluctuate.

[0010] In addition, it is known that the oxidation rate of the (110)plane, which is the sides of the trench, is 30 to 100% higher than thatof the (100) plane on the bottom. Therefore, a problem arises whereinthe inversion voltage of the channel region increases when the thicknessof the gate oxide film on the sides of the trench increases, leading tothe reduction of the driving performance of the MOS transistor.

[0011] Furthermore, there is a problem with the reliability of the gateoxide film in the (111) plane of the connection regions wherein aninsulation breakage electrical field is lower than that in the (100)plane on the bottom.

[0012] In addition, according to the conventional thermal oxidationmethod, the closer to the right angle the angle (i.e., the angle betweenthe sides and the bottom) in the crossing portion (connection region) ofthe surfaces of the silicon substrate having different plane directionsis the more significant is the reduction in the film thickness of thegate oxide film formed in the crossing portion. Therefore, it isnecessary to increase the curvature of the crossing portion and to makethe angle between the sides and the horizontal surface greater than 90°.As a result, the projection area of the crossing portion increases;therefore, the dimensions of the semiconductor device increase and theintegration of the devices throughout the LSI is decreased.

SUMMARY OF THE INVENTION

[0013] The present invention provides a semiconductor device comprising:a silicon based semiconductor substrate provided with a step includingan non-horizontal surface, a horizontal surface and a connection regionfor connecting the non-horizontal surface and the horizontal surface; agate insulating film formed in at least a part of the step; and a gateelectrode formed on the gate insulating film, wherein the entirety or apart of the gate insulating film is formed of a silicon oxynitride filmthat contains a rare gas element at a area density of 10¹⁰ cm⁻² or morein at least a part of the silicon oxynitride film.

[0014] The present invention also provides a manufacturing method for asilicon oxynitride film, comprising exciting plasma in an atmospherethat contains a gas including nitrogen atoms in molecules, oxygen and arare gas, thereby forming a silicon oxynitride film that contains a raregas element at a area density of 10¹⁰ cm⁻² or more on a silicon basedsemiconductor substrate provided with a step including an non-horizontalsurface, a horizontal surface and a connection region for connecting thenon-horizontal surface and the horizontal surface.

[0015] These and other objects of the present application will becomemore readily apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic view of a plasma unit using a radial lineslot antenna;

[0017] FIGS. 2 to 30 are schematic cross-sectional views showing stepsfor manufacturing semiconductor devices of the present invention;

[0018]FIG. 31 is schematic cross-sectional view of a semiconductordevice of the present invention;

[0019]FIG. 32 is schematic cross-sectional view of a semiconductordevice of the prior art;

[0020]FIG. 33 is a graph, showing plane direction dependencies ofinterface level densities by a radical oxynitriding for a semiconductordevice of the present invention and thermal oxidation;

[0021]FIG. 34 is a graph showing plane direction dependencies ofoxidizing rates by a radical oxynitriding for a semiconductor device ofthe present invention and thermal oxidation;

[0022]FIG. 35 is a graph showing plane direction dependencies ofinsulation breakage electrical fields by a radical oxynitriding for asemiconductor device of the present invention and thermal oxidation;

[0023]FIGS. 36A and 36B are views of showing cross-sectional TEMphotographs of corner portions by a radical oxynitriding for asemiconductor device of the present invention and thermal oxidation.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention provides a semiconductor device comprising:a silicon based semiconductor substrate provided with a step includingan non-horizontal surface, a horizontal surface and a connection regionfor connecting the non-horizontal surface and the horizontal surface; agate insulating film formed in at least a part of the step; and a gateelectrode formed on the gate insulating film. Furthermore, the entiretyor a part of the gate insulating film is formed of a silicon oxynitridefilm that contains a rare gas element at a area density of 10^(10 cm) ⁻²or more in at least a part of the silicon oxynitride film.

[0025] The silicon based semiconductor substrate that can be utilized inthe present invention is not in particular limited, and examples thereofinclude a silicon substrate, a silicon germanium substrate and the like.It is preferable for the silicon based semiconductor substrate to have por n conductive type. Examples of impurities for providing the pconductive type include boron, boron fluoride and the like, and examplesof impurities for providing n conductive type include phosphorous,arsenic and the like.

[0026] The semiconductor substrate is provided with a step including thenon-horizontal surface, the horizontal surface and the connection regionfor connecting the non-horizontal surface and the horizontal surface.The sides of the step correspond to a pair of non-horizontal surfaces,the bottom thereof corresponds to the horizontal surface and the regionsbetween the sides and the bottom correspond to a pair of connectionregions, for example, in the case of a trench. Furthermore, in general,the non-horizontal surface corresponds to a (110) plane of thesubstrate, the connection regions correspond to a (111) plane and thehorizontal surface corresponds to a (100) plane in the case of a siliconbased semiconductor substrate. It is noted that examples of the stepother than the trench include a wall form, a pillar form and the like.

[0027] Although the height of the step is not in particular limited, 0.1to 0.5 μm is preferable. In addition, in the case where the step isformed using a trench, it is preferable for the width of the trench tobe the minimum width that can be formed according to themicro-fabrication technique. Furthermore, it is preferable for the widthof the connection region projected onto a horizontal surface to be ⅓ to{fraction (1/10)} of the minimum width that can be formed according tothe micro-fabrication technique while it is preferable for the width ofthe connection region projected onto a surface that is perpendicular tothe horizontal surface to be ⅓ to {fraction (1/10)} of the minimum widththat can be formed according to the micro-fabrication technique.

[0028] According to the present invention, a gate insulating film isformed on at least a part of the step. According to the presentinvention, the gate insulating film includes the silicon oxynitride filmthat contains a rare gas element at a area density of 10¹⁰ cm⁻² or morein at least a part of the gate insulating film.

[0029] Herein, the gate insulating film is not particularly limited aslong as it is formed on at least a part of the step, and can be formed:solely on the non-horizontal surfaces, the connection regions or thehorizontal surfaces; or on both sides of the non-horizontal surfaces andthe connection regions, on both sides of the connection regions andhorizontal surfaces, or on the entire surface of the step. It ispreferable to form the gate insulating film on the entire surface of thestep from among the above because the formation process can besimplified.

[0030] Furthermore, the entirety or a part of the gate insulating filmis formed of the silicon oxynitride film, and examples of the gateinsulating film other than the silicon oxynitride film include a siliconoxide film, a silicon nitride film and the like. In addition, it ispreferable for the silicon oxynitride film to be formed at a position soas to make contact with at least the gate electrode.

[0031] In addition, the rare gas element may be included in at least apart of the silicon oxynitride film and may be included in the entiresurface of the silicon oxynitride film. Herein, it is preferable for therare gas element to be Kr or Ar from the point of view of the radicalgeneration efficiency that contributes to oxynitridation. In the casewhere the area density of the rare gas element is less than 10¹⁰ cm⁻²,stoichiometry composition of the silicon oxynitride film is far from theideal composition and the generation rate of the silicon oxynitride filmis lowered to a great degree restricting the desired performance frombeing exercised, and therefore, such a case is not preferable. Morepreferable area density is 10¹⁰ cm⁻² or more. It is noted that the areadensity. is measured by means of a secondary ion mass spectrometer(SIMS) and can be set at a predetermined value by adjusting themanufacturing conditions such as flow amount of the rare gas, DC bias,RF power and degree of vacuum.

[0032] An example of a method for forming the silicon oxynitride filmthat includes a rare gas element includes a method for directly andsimultaneously oxidizing and nitriding Si atoms that form the siliconbased semiconductor substrate in an atmosphere that includes, forexample, nitrogen gas or a compound gas containing nitrogen atoms,oxygen gas and a rare gas. In particular, it is preferable to carry outoxidation and nitridation while exciting plasma by means of microwaves.

[0033] The method of exciting plasma by microwaves is not particularlylimited as long as the microwaves can be introduced into a processchamber and examples thereof include known methods, for example, aplasma unit that uses a radial line slot antenna.

[0034] In addition, examples of the compound gas containing nitrogenatoms include NH₃ and the like.

[0035] In the case where the rare gas is Kr and the compound gascontaining nitrogen atoms is NH₃, it is preferable for the flow ratio ofthe respective gases in the atmosphere to be 89 to 99%/0.1 to 10%/1 to10% (Kr/NH₃/O₂).

[0036] It is preferable for the frequency of the microwaves being usedto be in the range from 900 MHz or more to 10 GHz or less.

[0037] In particular, it is preferable to form the silicon oxynitridefilm by using a high density plasma excited by microwaves when the lowsubstrate temperature is at 550° C. or less (e.g., 200 to 550° C.). Thatis, a single species of O radicals, a mixture of O radicals and NHradicals, or a mixed nitriding species of O radicals, N radicals and Hradicals are provided to the silicon based semiconductor substrate so asto oxynitride silicon, so that a thin silicon oxynitride film, havingsilicon-insulating film interface characteristics and current leak-proofcharacteristics equal to or better than those of the silicon oxide filmformed by means of known thermal oxidation and having excellentcharge-to-breakdown characteristics, can be formed at a temperature aslow as 550° C. or less (e.g., 400 to 500° C.). Roughness of theinterface between the silicon based semiconductor substrate and thesilicon oxynitride film can be greatly reduced by forming the siliconoxynitride film according to the above-described method, so that theelectron mobility in the surface of the silicon based semiconductorsubstrate can be greatly increased.

[0038] It is possible to change, in the depth direction, the oxygenconcentration peak and/or nitrogen concentration peak in the siliconoxynitride film by changing the flow ratio of nitrogen gas or thecompound gas containing nitrogen atoms to oxygen gas during theformation of the silicon oxynitride film.

[0039] Next, a gate electrode is formed on the gate insulating film.Examples of the gate electrode include metal layers such as of aluminumor copper, polysilicon layers, silicide layers such as of high meltingpoint metals (titanium, tungsten or the like), laminations of these, andthe like. In addition, the gate electrode may cover the entire surfaceof the step or may cover a part of the gate insulating film as long asit is positioned on the gate insulating film.

[0040] The silicon oxynitride film is formed into a gate insulating filmaccording to the above-described technique, so that the interface leveldensity of the (111) plane (approximately the same as the non-horizontalsurface) in the plane direction of the silicon based semiconductorsubstrate in the connection region can be greatly reduced in comparisonwith a conventional thermal oxidation method so as to be atapproximately the same level as that of the (100) plane at the bottom asshown in FIG. 33. As a result, reduction in the mobility of the carriersin the non-horizontal surface and fluctuation of the threshold voltagein the trap site can be suppressed. It is noted that the interface leveldensity of FIG. 33 has a value that is calculated based on the C-Vcharacteristics of an aluminum gate MOS capacitor.

[0041] In addition, the oxidation rate of the (111) plane (approximatelythe same as the non-horizontal surface) of the connection region isapproximately the same as that of the (100) plane of the horizontalsurface until the film thickness becomes of a certain value as shown inFIG. 34. Therefore, an increase in the channel inverting voltage due tothe increase in the film thickness of the gate oxide film on thenon-horizontal surface can be suppressed so that the driving performancecan be enhanced. The measurement of the film thickness in FIG. 34 iscarried out by an optical method.

[0042] Thus, as shown in FIG. 35, the insulation breakage electricalfield in the (111) plane of the connection region increases incomparison with the oxide film according to a thermal oxidation methodand the reliability of the gate insulating film can be increased. It isnoted that the insulation breakage electrical field of FIG. 35 indicatesa value measured on a MOS capacitor having a film thickness of 5 nmusing a determination current of 1 A/cm². In the figure, Kr/O₂ indicatesthe method of the present invention and Dry indicates the-conventionalthermal oxidation method.

[0043] In addition, as shown in the cross-sectional TEM photographs ofFIGS. 36A and 36B, the oxide film (FIG. 36A) in the connection regionaccording to the present invention is uniform in comparison with theoxide film according to a thermal oxidation method (FIG. 36B) and thedegree of integration of the LSI can be increased by removing theslopes.

[0044] It is noted that the semiconductor device of the presentinvention is applicable for a MOS transistor or a memory cell whereinthe gate electrode and the corresponding channel region include at leasta part of the non-horizontal surface.

[0045] Embodiment 1

[0046] First, a method for forming a silicon oxynitride film at a lowtemperature using plasma will be described below. FIG. 1 is a schematiccross-sectional view showing one example of a unit using a radial lineslot antenna, for forming a silicon oxynitride film.

[0047] Kr is utilized as a plasma exciting gas for the formation of asilicon oxynitride film according to the present embodiment. A vacuumcontainer (process chamber) 21 is vacuumed and Kr gas, NH₃ gas and O₂gas are introduced from a shower plate 22 to the process chamber whereinthe pressure is set at approximately 1 Torr. A substrate 23, in acircular form, such as a silicon wafer is placed on a sample support 24having a heating mechanism, and setting is carried out so that thetemperature of the sample becomes approximately 400° C.

[0048] 2.45 GHz microwaves are transmitted into the process chamberthrough a radial line slot antenna 26 and through a dielectric plate 27from a coaxial wave guide 25, so that high density plasma is generatedin the process chamber 21. The distance between the shower plate 22 andthe substrate 23 is set at 60 mm. As this distance is reduced, it ispossible for the rate of film formation to become higher. The siliconoxynitride film formed in the above-described conditions includes Kr ata area density of 10¹⁰ cm⁻² or more.

[0049] Thus, the inclusion of Kr at a area density of 10¹⁰ cm⁻² or morecontributes to the improvement of electrical characteristics and thereliability of the silicon oxynitride film. Concretely, they areconsidered to be improved because of the following reasons.

[0050] First, nitrogen hydrogen NH* in atom form and oxygen O* in atomform are efficiently generated due to krypton Kr* in atom form that isin intermediate excitation condition in a high density excitation plasmaof a mixed gas of Kr, NH₃ and O₂ (* indicates that it is a radical).These NH radicals nitride the surface of the substrate while the Oradicals, simultaneously oxidize the same. It becomes possible,according to the silicon oxynitridation of the present embodiment, toform a high quality silicon oxynitride film at a low temperature in the(100) plane, in the (111) plane and in the (110) plane of silicon, norelation to of the plane direction of silicon.

[0051] Furthermore, stress is relieved in the silicon oxynitride film orin the interface between the silicon semiconductor substrate and thesilicon oxynitride film; therefore, fixed charge and the interface leveldensity in the silicon oxynitride film are reduced. As a result,electrical characteristics and the reliability are greatly improved.

[0052] Embodiment 2

[0053] Next, a first embodiment of the semiconductor device (MOStransistor) of the present invention shown in FIG. 9 will be describedin detail. Although an example of an NMOS transistor will be describedbelow, a similar embodiment can be obtained by replacing it with a PMOStransistor.

[0054] First, ion implantation 2 is carried out on silicon substrate 1under the implantation conditions of 10 to 60 KeV and 5e12 to 5e13ions/cm² of, for example, boron or BF₂ as shown in FIG. 2.

[0055] Next, the resist is patterned by using a lithographic techniqueas shown in FIG. 3 so as to obtain a resist pattern 3.

[0056] Then, the silicon substrate 1 is removed through etching to thedepth of approximately 120 to 500 nm so as to form a trench as shown inFIG. 4. After that, the resist pattern 3 is removed.

[0057] Next, as shown in FIG. 5, a gate oxynitride film (siliconoxynitride film) 4 is formed so as to have a film thickness ofapproximately 10 to 16 nm according to a method using Kr plasma excitedby microwaves in the same manner as in Embodiment 1.

[0058] Then, a polysilicon layer 5 is filled into the trench as shown inFIG. 6. Furthermore, etching back is carried out until the corners ofthe top portion of the trench are completely exposed, thereby forming atrench-type gate 6 as shown in FIG. 7.

[0059] After that, ion implantation 7 is carried out under theconditions of 5 to 40 KeV, 1e14 to 1e16 ions/cm² of, for example,arsenic, as shown in FIG. 8.

[0060] Next, annealing is carried out at 800 to 900° C. for the purposeof recovering crystal in the implantation regions, driving in andactivating the implanted impurities, thereby forming a source 8 and adrain 9 as shown in FIG. 9. The NMOS transistor of the present inventionis manufactured according to the above-described process.

[0061] Embodiment 3

[0062] A second embodiment of the semiconductor device (MOS transistor)of the present invention will be described below in detail. Although anexample of an NMOS transistor will be described below, a similar examplecan be obtained by replacing it with a PMOS transistor.

[0063] First, the ion implantation 2 is carried out on the siliconsubstrate 1 under the implantation conditions of 10 to 60 KeV and 5e12to 5e13 ions/cm² of, for example, boron or BF₂ as shown in FIG. 10.

[0064] Next, a silicon oxide film 11 and a silicon nitride film 12 areformed on the silicon substrate 1 as mask materials at the time ofetching the silicon substrate 1. Furthermore, the silicon nitride film12 and the silicon oxide film 11 are patterned using the resist pattern3 (FIG. 11).

[0065] Next, a trench is formed by removing the silicon substrate 1through etching to a depth of approximately 120 to 500 nm as shown inFIG. 12. After that, the resist pattern 3 is removed.

[0066] Then, the gate oxynitride film (silicon oxynitride film) 4 isformed by means of oxynitridation of silicon using the above-describedKr plasma excited by microwaves so as to have a film thickness ofapproximately 10 to 16 nm as shown in FIG. 13. This silicon oxynitridefilm 4 includes Kr at a area density of 10¹⁰ cm⁻² or more.

[0067] Next, the polysilicon layer 5 is filled into the trench as shownin FIG. 14.

[0068] Then, etching back is carried out until the surface of theabove-described mask materials are completely exposed, so that thetrench type gate 6 is formed as shown in FIG. 15. After that, thesilicon nitride film 12, which is a part of the mask materials, isremoved.

[0069] After that, as shown in FIG. 16, ion implantation 7 is carriedout under the implantation conditions of 5 to 40 KeV and 1e14 to 1e16ions/cm² of, for example, arsenic.

[0070] Next, annealing is carried out at 800 to 900° C. for the purposeof recovering crystal in the implantation regions, driving in andactivating the implanted impurities, thereby forming the source 8 andthe drain 9 as shown in FIG. 17. The MOS transistor of the presentinvention is manufactured in accordance with the above-describedprocess.

[0071] Embodiment 4

[0072] A third embodiment of the semiconductor device (MOS transistor)of the present invention will be described in detail concerning the casewhere the non-horizontal surface of the silicon substrate shown in FIG.24 is utilized as a channel. Although an example of an NMOS transistorwill be described below, a similar example can be obtained by replacingit with a PMOS transistor.

[0073] First, the ion implantation 2 is carried out on the siliconsubstrate 1 under the implantation conditions of 10 to 60 KeV and 5e12to 5e13 ions/cm² of, for example, boron or BF₂ as shown in FIG. 18.

[0074] Next, the silicon oxide film 11 and the silicon nitride film 12are formed on the silicon substrate 1 as mask materials at the time ofetching the silicon substrate. Furthermore, the silicon nitride film 12and the silicon oxide film 11 are patterned using the resist pattern 3(FIG. 19).

[0075] Then, as shown in FIG. 20, the entirety of the silicon substrate1 in the region where the target device is formed is etched to a depthof approximately 120 to 500 nm except the region where theabove-described mask materials remain. As a result, a pillar formstructure can be formed in the silicon substrate.

[0076] Next, the resist pattern 3 is removed.

[0077] Furthermore, as shown in FIG. 21, the gate oxynitride film(silicon oxynitride film) 4 is formed by oxynitriding the silicon usingthe above-described Kr plasma excited by microwaves so as to have a filmthickness of approximately 10 to 16 nm. This silicon oxynitride film 4includes Kr at a area density of 10¹⁰ cm⁻² or more.

[0078] Next, the polysilicon layer 5 is deposited as shown in FIG. 22.

[0079] Furthermore, etching back is carried out until the surface of theabove-described mask materials are completely exposed, so that the gate6 is formed on the side walls (non-horizontal surfaces) having a pillarform structure in the silicon semiconductor as shown in FIG. 23.

[0080] After that, the ion implantation 7 is carried out under theimplantation conditions of 5 to 40 KeV and 1e14 to 1e16 ions/cm² of, forexample, arsenic after the removal of the silicon nitride film 13 whichis a part of the mask materials. Next, annealing is carried out at 800to 900° C. for the purpose of recovering crystal in the implantationregions, driving in and activating the implanted impurities, thereby,forming the source 8 and the drain 9 (FIG. 24). The MOS transistor ofthe present invention having the channel region in the non-horizontalsurface is manufactured according to the above-described process.

[0081] Embodiment 5

[0082] A forth embodiment of the semiconductor device (MOS transistor)of the present invention shown in FIG. 31 will be described below indetail. Although an example of an NMOS transistor will described below,a similar example can be obtained by replacing it with a PMOStransistor.

[0083] First, ion implantation is carried out on the silicon substrate 1under the implantation conditions of 10 to 60 KeV and 5e12 to 5e13ions/cm² of, for example, boron or BF₂ as shown in FIG. 25. Furthermore,the drain region 9 is formed by carrying out ion implantation under theconditions of 5 to 40 KeV and 1e14 to 1e16 ions/cm² of arsenic and thesource region 8 is formed by carrying out an ion implantation under theconditions of 300 to 800 KeV and 1e13 to 5e14 ions/cm² of phosphorous orarsenic.

[0084] Next, the silicon oxide film 11 and the silicon nitride film 12are formed on the silicon substrate 1 as mask materials at the time ofetching the silicon substrate. Furthermore, the silicon nitride film 12and the silicon oxide film 11 are patterned by using the resist pattern3 (FIG. 26).

[0085] Then, as shown in FIG. 27, the silicon substrate 1 is removedthrough etching to a depth of approximately 120 to 500 nm by using ananisotropic etchant which makes the etching rate for the (111) plane inthe silicon crystal plane direction the lowest, so that a trench in aV-shape oriented in the (111) plane is formed.

[0086] After that, the resist pattern 3 is removed. Next, as shown inFIG. 28, a gate oxynitride film (silicon oxynitride film) is formed byoxynitriding the silicon using the above-described Kr plasma excited bymicrowaves so as to have a film thickness of approximately 10 to 16 nm.This silicon oxynitride film 4 includes Kr at a area density of 10¹⁰cm⁻² or more.

[0087] Next, the polysilicon layer 5 is filled into the trench as shownin FIG. 29.

[0088] Furthermore, etching back is carried out until the surfaces ofthe above-described mask materials are completely exposed, so that thetrench type gate 6 is formed as shown in FIG. 30. The MOS transistor ofthe present invention is manufactured according to the above-describedprocess. The channel in this embodiment is formed in the area indicatedby “a” in FIG. 31.

[0089] According to the present invention, it is possible to provide asemiconductor device formed on a three dimensional substrate with a stepincluding non-horizontal surfaces, horizontal surfaces and connectionregions for connecting the non-horizontal surfaces and horizontalsurfaces, thereby solving serious disadvantages in characteristics ofthe semiconductor device, such as reduction in mobility of carriers andfluctuation in threshold voltage caused by the existence of an interfacelevel in the non-horizontal surfaces and in the connection regions.

[0090] In addition, oxynitridation rate of the non-horizontal surfacesin the (110) plane and of the connection regions in the (111) plane inthe trench form is equal to that of the horizontal surfaces in the (100)plane; therefore, an increase in the driving performance of thesemiconductor device becomes possible as a result of uniformed filmthickness in the entire region of the surface of the gate oxynitridefilm (silicon oxynitride film). In addition, the reliability of the gateoxynitride film disposing the surfaces of the substrate in the non-(100)planes such as, the (110) plane and the (111) plane can be increased tothe same level as that of the horizontal surfaces in the (100) plane.

[0091] As a result of this, an increase in the driving performance ofthe three dimensional semiconductor device and enhanced reliability canbe achieved.

What is claimed is:
 1. A semiconductor device comprising: a silicon based semiconductor substrate provided with a step including an non-horizontal surface, a horizontal surface and a connection region for connecting the non-horizontal surface and the horizontal surface; a gate insulating film formed in at least a part of the step; and a gate electrode formed on the gate insulating film, wherein the entirety or a part of the gate insulating film is formed of a silicon oxynitride film that contains a rare gas element at a area density of 10¹⁰ cm⁻² or more in at least a part of the silicon oxynitride film.
 2. A semiconductor device according to claim 1, in which the rare gas element is Kr or Ar.
 3. A semiconductor device according to claim 1, in which the silicon oxynitride film is a film formed by simultaneously oxidizing and nitriding the silicon based semiconductor substrate.
 4. A semiconductor device according to claim 1, in which the silicon oxynitride film is a film formed on the silicon based semiconductor substrate in an atmosphere that includes a nitrogen gas or a compound gas containing nitrogen atom, oxygen gas and a rare gas and introduces microwaves.
 5. A semiconductor device according to claim 4, in which the compound gas containing nitrogen atom is NH₃.
 6. A semiconductor device according to claim 4, in which the horizontal surface corresponds to a (100) plane in the silicon based semiconductor substrate, the connection regions correspond to a (111) plane in the silicon based semiconductor substrate and the non-horizontal surface corresponds to a (110) plane in the silicon based semiconductor substrate.
 7. A semiconductor device according to claim 4, in which the silicon based semiconductor substrate has a trench comprising a pair of non-horizontal surfaces, a pair of connection regions and the horizontal surface, the gate insulating film is the silicon oxynitride film formed on the entire surface of the trench and contained the rare gas element at the area density of 10¹⁰ cm⁻² or more, the gate electrode is filled into the trench.
 8. A manufacturing method for a silicon oxynitride film, comprising exciting plasma in an atmosphere that contains a gas including nitrogen atoms in molecules, oxygen and a rare gas, thereby forming a silicon oxynitride film that contains a rare gas element at a area density of 10¹⁰ cm⁻² or more on a silicon based semiconductor substrate provided with a step including an non-horizontal surface, a horizontal surface and a connection region for connecting the non-horizontal surface and the horizontal surface. 